Preparation of a valuable final product of substantially constant quality



June 30, 1964 J DE KONING ETAL 3,139,269

PREPARATION OF A VALUABLE FINAL PRODUCT OF SUBSTANTIALLY CONSTANT QUALITY Filed July 17. 1958 5 Sheets-Sheet 2 F I INVENTORS' JACOB DE NING BAUKE 8.3 .SWERDA ATTORNEYS June 30. 1964 J, DE KONING ETAL 3,139,269

PREPARATION OF A VALUABLEI FINAL. PRODUCT OF SUBSTANTIALLY CONSTANT QUALITY Filed July 17, 1958 5 Sheets-Sheet 3 FIG. 5 206 I FIG 6 8 i 7 7 2175 United States Patent 3,139,269. PREPARATION OF A VALUABLE FINAL PRODUCT 0F SUBSTANTIALLY CONSTANT QUALITY Jacob de Koning and Bauke S. Sieswerda, Geleen,

Netherlands, assignors to Stamicarbon N.V., Heel-- len, Netherlands Filed July 17, N58, Ser. No. 749,136 Claims priority, application Netherlands July 29, 1957 6 Claims. (Cl. 259-4) The present invention relates to the preparation of a valuable final product of substantially constant quality, containing at least one component the content of which in the product determines the quality thereof and more particularly to a method and apparatus wherein such product is obtained from a raw starting product by separating the latter in an upgrading plant, by means of one or more separatory devices, into two or more fractions differing in their contents of the component(s), and the component content is substantially continuously measured in one of the fractions having a mean component content which substantially does not exceed a predetermined admissible value.

The expression valuable produc or final product is herein used to distinguish this product from the other fraction or fractions coming from the separating plant, which fractions are either removed as waste material or are to be subjected to an after-treatment.

An example of such a separation is the preparation of a salable final product from raw coal, where the ash content determines the quality of the final product. ash' content depends on the amount of shale contained in the coal. As the content of shale determines the specific gravity of the coal, the required final product is obtained by separating according to a given specific gravity in one or more separatory devices of a type normally used for this purpose, as, for example, jigs, rheowashers, heavymedium washers and the like.

Both the seller and the buyer want the coal obtained in this way to have an ash content which approximates the guaranteed ash content as closely as possible. Not only does the buyer wish to receive a coal whose ash content does not exceed the guaranteed content, but an ash content lower than the guaranteed content may likewise be undesirable, as this may lead to unpleasant surprises. For instance, in the blast furnace industry a coke of constant ash content will be desired, as fluctuations in the ash content of the coke necessitate fluctuations in the additions to the ore. Therefore, the task of a coal preparation plant in the mining industry is to prepare a product having an ash contentequal to or lower than the value agreed upon. It is preferable to deliver a product having an ash content which is as close as possible to the maximum value agreed upon, since the delivery of each lot with an ash content lower than this value means a diminishing of the proceeds. Even tenths of a percent are significant in this connection.

Theoretically it would be possible, by a correct adjustment of the specific gravity of separation in the washing process, to obtain a product with an ash content approximating rather closely to the maximum content agreed upon, since the ash content of coal substantially determines the specific gravity of separation which is to be applied in the washing process. A separation according to constant specific gravity does not at all insure a constant ash content of the coal because, the particles having a specific gravity only slightly lower than the specific gravity of separation have a considerably higher ash'content than the particles having a substantially lower specific gravity. Therefore, the ash content of the washed coal depends to a large extent on the composition of the raw product. In addition, the specific gravity of separation exactly the prescribed maximum ash content.

quently, greater or smaller portions of the product to be 3,139,269 Patented June 30, 1964 "ice is determined by some other factors, as for example, by the washing properties of the coal. Thus, the quality of the coal delivered to the coal preparation plant has an important influence. This quality is subject to great fluctuations, which are, in part, due to variations of the percentage of shale present in the coal. These Variations upset the adjustment of the washing process and are the cause of a product being delivered which deviates considerably from that desired, as readjustment takes much time. Owing to the causes mentioned above, the ash content of the delivered product may be subject to considerable variations. Fluctuations between 4% and 12% are by no means rare, even if the separation process is adjusted to a constant specific gravity.

As a result of these fluctuations it is practically impossible to deliver a product that has exactly or almost Consedelivered will have lower ash contents and other portions higher ash contents than the content agreed upon, so that, in order to avoid refusal of delivered coal, a wide margin will be maintained between the ash content of the delivered product and the permissible ash content agreed upon, which, as already stated, means a considerable loss to the colliery. Furthermore, the buyer will often prefer to receive a product having an ash content which is as constant as possible. This is true particularly for coking coals, the coke from which is to be used in blast furnaces. Strong fluctuations in the ash content of the coke may be very awkward in the blast furnace industry.

In the interest of both the buyer and the seller it is desirable, therefore, to prepare a product which is as constant as possible, the ash content approaching as closely as possible to the guaranteed content.

It has already been proposed by means of a continuous measurement of the product coming from the washing plant and by making use of the values obtained from this measurement, so to control the washing appliances that,if the measured ash content should be too high, washing is continued at a lower specific gravity, and vice versa. Such a procedure may be carried out, for example, by means of a measuring instrument emitting and receiving electron, electromagnetic, light, X-ray beams or the like. This measuring device which, in a sample continuously drawn from the stream of washed valuable product, measures, in a very short time, values continuously which are very closely correlated with the ash content, can emit impulses which actuate a mechanism controlling the operation of the washing plant. Owing to the lag in the adjustment of the washing plant or the specific gravity of the washing medium, the results of such a process, especially when used for washing coal, cannot be expected to be very good, partly because of the large fluctuations in the composition of the feed of the raw product, and hence also of the product delivered, which fluctuations often occur within a short time. Irrespective of practical difficulties involved in adjusting the washing devices so that a constant ash content is obtained, increased proceeds are obtained if washing is carried out as much as possible to a constant specific gravity. For, in one case particles of rather high ash content are added to the coal in order that the mean ash content may be sufficiently high, and in the other particles having a considerably lower ash content are removed in order to prevent the mean ash content from becoming too high. At the same time, the increased proceeds are not obtained, for the reason mentioned above.

The present invention is based on the surprising realization that it is better to alter the adjustment of the washing plant or the washers as little as possible, hence to separate as much as possible to a constant specific gravity, and to find the solution of the problem in an improvement 3 of the material stream as this comes from the upgrading plant as a product ready for delivery, without subjecting this stream to another washing procedure. According to the invention, the solution of thisproblem is found by mixing portions of the substantially continuously measured fraction coming from the separatory device which have a content lower than the admissible content, with reference to this measurement with an amount of material having a higher content than is admissible sufficient to obtain a mixture substantially brought at the admissible content.

Preferably, the material is divided, in response to the measurement, into at least two fractions of which at least one has a content higher than is admissible, which fraction is mixed-according to requirement with the portions having a content lower than the admissible content. If this measure is used one or more fractions remain whose content is smaller than or at most equal to the admissible content, the content of which fractions is brought as close as possible to the admissible content by admixing'material having a higher content than is admissible. As noted above, those separated-01f fractions which have a content higher than is admissible will be used for this admixing.

In this way the advantage is obtained that in the separatory device a separation can be carried out to a content which theoretically approximates very closely to the admissible content.

The process according to the invention can be carried out in various ways. In one way of realizing it in accordance with the invention, the material is divided into anumber of fractions having predetermined different contents (or a maximum and/ or a minimum content each), from which fractions the final product is obtained by controlled mixing. In this way a number of fractions is obtained the content of each of which may lie within close limits, such fractions being divided into fractions the mean content of which is higher than the admissible value and fractions the mean content of which is below this value. By a suitable mixing of these fractions a final product of constant quality, and having a content which approximates very closely to the admissible content, may be obtained.

The measuring instrument may be of the type described above, or it may be of any other type, provided it measures the content of the substance determining the quality of the final product immediately, i.e. with a negligible time lag (e.g. an incinerating device). Preferably the fractions separated in this way will be collected in separate collecting chambers, for example, bunkers. The controlled mixing of the resulting fractions is carried out with reference to a substantially continuous measurement of the final product to be delivered, which measurement determines the discharge from the collecting spaces of two or more of the collected fractions. This measurement may be carried out on the stream of the mixed final product by means of a similar measuring device as described above.

According to a different manner of performing the process, the addition of material having a higher content than is admissible is made to the stream'of material coming from the separating or upgrading plant. In this case the stream of material coming from the separatory device is sampled and the content of the component determining the value of the product is measured as described above. However, only the fraction of this stream having a higher content of the component than admissible is separated oif. Preferably, the separated-off fractions are used as adding material to those fractions of the stream whereof the content is lower than admissible.

However, the separation in the separatory device may also be carried out in such a way that the stream of the upgraded product containsno portions or only few portions having a content higher than admissible. In a coal preparation plant this may be effected, for instance, by separating to a low specific gravity. In this case the I in the case of coal, for example, the mixed fraction, has

a higher ash content and consequently can be used only as a less valuable fuel, for example, as boiler fuel. However, this fraction may still contain considerable quantities of particles of comparatively low ash content. As boiler fuel, these quantities have little value, but when admixed to a high-quality fuel they naturally have a higher value. It is already known to effect, in a trough of triangular section, a layer separation according to specific gravity in the mixed fraction, the particles having the highest specific gravity, and hence the highest ash content, lying on the bottom and the specific gravity as well as the ash content gradually decreasing in upward direction. In admixing part of this fraction to the fraction of low ash content it will be preferred to separate off the upper layers as much as possible and to use these in mixing.

Accordingly, it is an object of the present invention to provide aprocess of the type described which is simple, efficient and economical.

Another object of the present invention is the provision of an apparatus for carrying out the above described process which is made up of simple and, for the most part, individually well known components capable of simply, economically, and efficiently obtaining a final product of substantially constant quality.

These and other objects of the present invention will become more apparent during the course of the following detailed description and appended claims.

The invention can best be understood with reference to the accompanying drawings wherein illustrative embodiments are shown.

In the drawings:

FIGURE 1 is a diagram of a plant according to the invention;

FIGURE 2 is a diagram of a control element of a bunker gate;

FIGURE 3 is a diagram of a detail of the element according to FIGURE 2;

FIGURES 4a and 4b comprise a circuit diagram of the transmission of the impulses to the control element of the gates;

FIGURE 5 is a diagram of a different apparatus according to the invention; and

FIGURE 6 is part of a graph on which are recorded, by means of a measuring instrument, the ash contents of a stream of coal issuing from a separatory device.

Referring more particularly to the drawings, there is diagrammatically illustrated in FIGURE 1 a separating plant, generally indicated at 1, which may be a coal preparation plant of a colliery. The final product, destined to be delivered, is fed into a number of bunkers 3-7 by means of a conveyer 2, which, as shown is a scraper chain. At the top of each bunker there is a gate, 9-13, the flap of which can turn on a spindle 8. At the bottoms of the bunkers there are gates 14-18. In the bottom of the conveyor, at 19, there is a narrow slot or a number of apertures, through which can flow a continuous small stream of the material passed over the slot or over the openings. This stream is collected on a conveyor belt (not shown) moving at uniform velocity, which belt carries the sample thus obtained to a grinding plant (not shown) and next to a drying plant (not shown), from where the material is passed, as a layer of uniform dimensions, through abeam of X-rays. By means of these X-rays the ash content is measured and recorded with a negligible time lag. This measuring device, re-

ferred to by 20, can, at certain recorded values, emit an impulse capable of influencing a mechanism. In the case under consideration one or more of the gates 9-13 are closed or opened, as will be more fully explained hereinafter. It will be clear that by using the emitted impulses the bunkers can so be filled that each of them contains a material the ash content of which lies within narrow limits. Of course, it is also possible with reference to the recorded values of the ash content to operate the bunker gates manually or to use remote control by means of a push-button system.

Under the bunkers there is a discharge device 23, which as shown is a belt conveyor. By opening two or more bunkers a mixture can be formed having an ash content which very closely approaches the guaranteed content or is practically equal to it. By means of a mixing device 24-which may be of any desired type and may consist, e.g., of two or more belt conveyors so placed with respect to each other that the material falls from one belt onto the othera homogeneous mixture is prepared, which by means of a conveyor 25, is transported to the delivery place. Adjacent the conveyor 25 there is a further measuring instrument 26, which operates in a similar manner to the instrument 20, to determine the ash content of the mixture on the conveyor 25. 1 The measuring instrument 26 emits impulses, in dependence on the fluctuations in the ash content of the said mixture, which operate one or more of the bunker outlet gates 14-18 in such a way that the composition of the mixture is corrected and the product finally delivered has an ash content which is substantially constant at the required predetermined value.

FIGURE 1 shows only the control line 21-22 for the gate 9 and the control line 27 for the gate 14 it being understood that all are similar. FIGURES 4a and 4b show a diagram of a circuit operating the inlet gates 9-13. To the indicator of the measuring instrument 20 there is coupled a disc cam 30 the profile of which is represented in FIG. 4a and includes a step 31 the position of which determines the positions of four microswitches A, B, C, D. The position of these switches at any given time consequently depends on the ash content of the coal on conveyor 2 at that time. The positions of the switches A, B, C, D can moreover be adjusted for varying the particular ash content values according to which the said coal fraction is divided over the different bunkers. In the particular case illustrated the switches were pre-set so as to respond at measured ash contents of 6, 7, 8 and 9% and when switch A is operated by the cam as shown in FIG. 4a, the switches B, C and D are at rest. FIG. 4b likewise shows the switches A-D. The alternative contact points of these switches are con nected with the lines 32 and 33 of an A.C. circuit having a voltage of eg 42 v., in such a way that of the successive switches the upper and lower contact points, alternately, are connected to the line 32, and the lower and upper contact points alternately are connected to the line 33.

Between the fixed contacts 34 and 35, 35 and 36, 36' and 37, there are coils 43, 44 and 45. In addition, there is a coil 42 between the contact point 34 and a line 55 connected to the line 32, and a further coil 46 between the contact point 37 and the line 56 connected to the line 32.

As will be described in more detail, each of the coils 42-46 has a movable metal core which is displaced when the coil is energized and as a result actuates the operating mechanism of a bunker gate. It can be seen that the five coils provided can operate the five bunkers,v or five groups of bunkers if one operating mechanism is capable of opening or closing more than one gate at a time.

The circuit also includes hand operated three-position switches indicated at E-F-G-H-K-L-M-N-O and P, the fixed contacts 59-68 of which are connected to the ends of the coils. If a switch is in the intermediate position, the

associated coil is connected to the automatic system; when a switch is turned to the left the associated coil is disconnected, while it is energized irrespective of the position of the associated one of the switches A-D when the switch is turned to the right by hand. The right-hand contacts of successive switches are connected, alternately, to an auxiliary line 57 and an auxiliary line 58, which are, in turn, connected through lines 69 and 70 with the lines 32 and 33, respectively. A deviation from this arrangement is seen in the right-hand contact point of switch P, which is connected to line 57.

The arrangement is such that each bunker inlet gate is closed only when the coil operating this gate is energized. When the coils 42-46 operate the gates 9-13, respectively the aforesaid hand-operated switches in their intermediate positions, and the switches A-D are operated at ash contents of 6, 7, 8 and 9% respectively, then in the position shown in FIGURES 4a and 4b, in which the switch A is pressed down, the current flows from the line 32 through line 55, coil 42, lines 47 and 38 and via switch A to line 33. Due to the position of switch B the circuit of coil 43 (line 32, switch B, lines 39 and 49, coil 43, lines 48, 38,.switch A, line 71, line 33) is open and consequently the inlet gate 10 of bunker 4 is open. Likewise it can be seen that the coils 44, 45 and 46 are also energized, so that the gates operated by them, viz. 11, 12 and 13 are' closed. If the current fails all the gates are opened.

If the cam 30 is displaced to beyond B, taking up a position intermediate between B and C, which is the case when an ash content of between 7 and 8% has been measured, it is seen from the diagram that the current passes through the coils 42, 43, 45' and 46, while only coil 44 is without current. It follows that gate 10 is closed when gate 11 is opened.

From the above it can be seen that only one gate is open at one time and that gate 9 will be open before switch A is pressed down, gate 10 is open when switch A is down, gate 11 is open when switches A and B are down, gate 12 is open when switches A, B and C are downand gate 13 is open when switches A, B, C and D are down. Thus assuming, as before, that switches A, B, C, and D are depressed at content percentages of 6, 7,. 8 and 9% respectively, itcan be seen that bunker 3 will receive coal having an ash content with a range up to 6%, bunker 4 will receive coal with an ash content ranging between 6% and 7%, bunker 5 will receive coal with an ash content ranging between 7% and 8%, bunker 6 will receive coal with anash content ranging between 8% and 9%, and bunker 7 will receive coal withan ash content ranging above 9%.

FIGURES 2 and 3 illustrate a preferred embodiment of a control mechanism for the gates. The mechanism is shown as gate 9, although it will be understood that each of the other gates are provided with a similar control mechanism. As best shown in FIGURE 2, the control mechanism includes a cylinder having a piston81 mounted therein for axial displacement by the action of a medium, such as air, forced into the cylinder under pressure. As indicated at 83, the outer end of a piston rod 82 is hinged to one end of a bar 84, the other end of which is fixed to the pivot 8 of the gate 9. When the piston 81 is displaced in the direction indicated by the arrow 85, the gate 9'is moved in the direction indicated by the arrow 86 and is thus closed. The medium under pressure is supplied and discharged through conduits 87 and 88, respectively, in dependence on the direction to which the piston is to be moved. The conduits 87 and 88 are connected to a control element 90, which conveys the medium supplied through conduit 89 to' one of the two conduits 87 and 88. A head 93 houses one of the coils 42-46, in this particular case coil 42, which is connected to the contact points 59 and 60 through the lines 91 and 92'. The control element diagrammatically shown in FIGURE 3 has a head 93 which'houses the 7 coil 42.

The control element comprises a housing 94 having a. sleeve or lining 95, in which a control slide valve 96 is axially displaced against the pressure of a spring 97 bearing against the lower end thereof. The displacement is effected by air under pressure controlled by means of a rod 98 which is concentric with the coil 42. The rod 98 can be axially displaced in a block 112 having a space 113 in the lower end thereof. The lower end of the rod 98 is provided with a flange 114, the upper side of which supports the lower end of a spring 115. The upper end of the spring 115 presses against the upper wall of the block space 113.

When in the position of rest, the flange 114 closes a passageway 116 in a body 117 mounted within a bore 118 formed in a cover 119 secured to the upper end of the housing 94. A passageway 120 communicates the bore 118 with a bore 99 in the housing 94. A passageway 125 connects the space 113 with a space 126 over the control slide valve 96. The rod 98 has axial grooves 121 formed therein which open into a closed space 124 in the coil. The top of this space is closed by a cylindrical block 122 which has an axial channel 123. The height of the space 124 is such that, if the rod 98 is drawn upwards as a result of the coil 42 being energized, the top of the rod 98 closes the channel 123.

The outlet side of the bore 99 is connected to the conduit 89 and the outlet side thereof communicates with the space within the lining 95 through a port 100. Bores 101 and 103 are connected on their inlet side to the space inside the lining, through ports 102 and 104, respectively, and on their outlet side to the atmosphere. Bores 105 and 106 in the opposite side of the housing have their outlets connected with conduits 87 and 88 respectively. The inlet sides of the bores 105 and 106 are connected, through ports 107 and 108, to the space inside the lining.

The control slide valve 96 has lands or ridges 109 and 110, 111 and 111', so located that in the position shown in the drawing, in which no current passes through the coil 42, the bore 99 is connected, through ports 100 and 107, to the bore 105, and the medium under pressure is conveyed, via conduit 87, to the lower side of the piston 81 (FIGURE 2) and the gate 9 is open. The bores 106 and 103 are interconnected and enable the conduit 88 to be evacuated.

When the coil 42 is energized the rod 98 is drawn upwards against the pressure of the spring 115, closes the channel 123 and connects the channel 116 to the space 113. Compressed air can now flow through the channel 120, the space 118, the channel 116, the space 113 and the channels 125 to the space 126. As a result the control slide valve 96 is pressed down against the pressure of the spring 97, so that connections are established between the bores 99 and 106 and between the bores 102 and 105. Medium under pressure flows through conduit 88 to the top of the piston 81 and presses it down, so that the gate 9 is closed while at the same time the conduit 87 is evacuated.

When the current through coil 42 is cut oflt, the rod 98 is pressed down by the spring 115, closes the channel 116 and opens the inlet of channel 123. The compressed air present in the space 113 can now escape through the grooves 121, the space 124 and the channel 123, so that the spring 97 can press upwards slide valve 96. The control device shown is available in the commercial market and is not claimed as novel per se herein.

Referring now more particularly to FIGURE 5, there is shown a modified form of an apparatus embodying the principles of the present invention. The apparatus includes a separatory means 201 which may be a separatory device or an upgrading plant comprising one or more separatory devices, e.g. a coal preparation plant, in which the raw product supplied at R is separated. A stream of coal from the upgrading plant obtained by separation of the raw product at a given specific gravity, if necessary after being subjected to an after-treatment in filters, driers,

etc., is represented at 202 as being conveyed for delivery at S. Another stream of coal coming from the same upgrading plant and having a mean ash content higher than the mean ash content of stream 202 is represented at 203 and is conveyed for'delivery at T. At 204 a continuous representative sample is drawn from the stream of coal 202, and is then fed on a trough or a belt conveyor 208, to a measuring instrument 205, operating e.g. with X- rays to measure the ash content. The measuring instrument emits an impulse along line 206 whenever a certain predetermined ash content is exceeded. The impulse opens a by-pass valve 207 in the path of the stream 202, which serves to divert the stream 202 when so opened thus separating from the stream the portions thereof having an ash content above the predetermined value. The valve is closed again to permit flow in stream 202 when the ash content drops below the said value. The distance between the sampling place 204 and the valve 207 is so chosen that the time needed for the transport of the'sample to the measuring instrument 205, the preparation of the sample and the measurement, is substantial- 1y equal to the time needed for a particle contained in the stream to travel from the position indicated at 204 to the valve 207.

Downstream from the valve 207 there is a mixing device 209, in which a portion of the material stream 203 can be admixed to the material stream 202. As close as possible to the mixing device 209, downstream from this device, there is an appliance 211 for continuous sampling, the sample being fed, through a trough or a belt conveyor 212, to a measuring instrument 213, which records the ash content and is capable of emitting impulses through a channel 214, thus controlling a distributing device 210 in the stream of material 203. This distributing device may be, for example, a so-called open-close valve which is controlled by a servomotor so that when the ash content recorded at 211 falls below a predetermined value, the valve is opened to divert the flow of stream 203 into the mixing device and it is not shut to permit the stream 203 to discharge at T before the ash content is exceeded.

FIGURE 6 shows part of a strip chart on which, by means of the measuring instrument 205, the ash contents of the samples drawn at 204 have been recorded. The vertical lines show the ash content, rising from 6 to 11%, the horizontal lines show the time division of the chart, in hours. The irregular line 215 shows the ash content measured. The diagram shows, in the first place, that, in spite of the fact that separation is made to a constant specific gravity, there are considerable variations in ash content. If it should be desired, for example, to deliver a material having an ash content of 8%, the portions of the stream of material denoted by 216 and 217 prove to have ahigher ash content, as can be seen from the diagram. By separating 0E these portions at 207 through the use of suitable conduit or conveyors and raising the ash content of those portions of the stream which have an ash content below 8% to this value by controlled mixing at 209, a stream of material of uniform ash content, substantially corresponding to the required ash content agreed upon, is obtained at S. The process according to the invention has the additional advantage that thebest portion of the stream 203 can be sold at a higher price. The material separated off at 207 may, if desired, be added to the stream of material 203 through the use of suitable conduit or conveyors. Instead of one mixing device 209 and one distributing device 210, several of these devices may be used, so that mixing proceeds more smoothly.

The X-ray measuring means 20, 26, 205, and 213, which are operative to emit an impulse for controlling valves 9-13, 14-18, 207 and 210 respectively, are wellltnown in the art, such measuring means being disclosed in British Patents Nos. 750,650 of June 20, 1956, 762,432 of November 28, 1956 and 768,534 of February 20, 1957.

It can thus be seen that there has been provided an apparatus which comprises an upgrading plant comprising one or more separatory devices for the raw product, and further of at least one measuring instrument, arranged beyond a separatory device or the upgrading plant, in the discharge means for an upgraded fraction, for example, an instrument emitting and receiving electron, light, electromagnetic, X-ray or suchlike beams, which instrument measures substantially continuously the content of the substance determinative of the quality in the product coming from this device or plant or at least in a sample drawn substantially continuously from this product, and which instrument can operate separating and/or mixing devices located in the discharge means and controlled by the said mechanism by emitting impulses depending on the content measured.

In one of the embodiments this mechanism controls one or more valves which are capable of closing or opening the feed means of the bunkers located in the said discharge means. As a rule the impulses emitted by the measuring device are electric impulses. According to the invention the impulse emitted at each pre-determined value of the measured content can be passed through a coil and thus displace a metal core, as a result of which the operating mechanism of the gate is actuated, the whole arrangement being such that only if a coil is actuated the gate connected with it is closed. In this way the advantage is obtained that when the operating current fails all the feed gates of the bunker system are open.

According to the invention, the discharge openings of the bunkers are connected to a mixing device, in the discharge mechanism of which device another measuring device working with a negligible time lag is provided, which measuring device operates means for controlling the amounts of material discharged from one or more bunkers.

The invention may be given a variety of embodiments. In the simplest of these, use is made of two bunkers one of which receives the material having a content of the substance determining the value which is above the permissible value, the other the material having a content below this permissible value, while the desired value is obtained by controlled mixing. It is also possible to work with three bunkers, the middle of which receives the material which has about the mean content, the others the material with a higher and a lower content than the mean.

It will be preferred to work with a greater number of bunkers. As described above, if one should desire, for instance, to deliver a coal having an ash content of between 7 and 8%, it is advisable to use five or more bunkers. It is possible, for instance, to store in separate bunkers coals with successive ash content, for example, a content lower than 6%, a content of between 6 and 7%, a content of between 7 and 8%, a content of between 8 and 9% and a content higher than 9%. This range may be extended according as more bunkers are available. It is possible, by adjusting the discharge of two bunkers to certain capacities, to obtain a mixture the ash content of which approaches the desired value, and to correct the deviations found by the measurement with coal from a bunker the contents of which have a higher, or lower, ash content.

Another possibility of forming a mixture of the correct ash content consists in the application of a control of the feed from two bunkers by means of a differential transmission controlled by a measuring device. It should be borne in mind that it is practically excluded that the material in a bunker has exactly the mean ash content lying between the two extreme values at which the gate of the bunker is opened and closed. Besides, the material flowing into the bunker forms layers differing in ash content.

However, the great advantage of the process according to the invention is not only the circumstance that a material with a constant quality very close to the correct value can be delivered, but also that it is possible to use a separatory treatment largely free of variations, to obtain the greatest possible yield. A change in the separating limit, e.g. in the specific gravity to which the Washing is performed, need be made only if after a longer period it should be found that the stock in the bunkers containing the product with either the lowest or the highest content of the component determining the quality has decreased too much.

In a different embodiment a mixing device controlled by the measuring instrument is provided in the discharge means, which mixing device is connected to a discharge device for a different fraction coming from the separatory device(s) or the upgrading plant.

It, thus will be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing specific embodiment has been shown and described only for the purpose of illustrating the principles of this invention and is subject to extensive change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

We claim:

1. A process of preparing a valuable final product of substantially constant quality, containing at least one component the content of which in the product is determinative of its quality, from a fraction, having a mean content of said component which substantially does not exceed a predetermined value, obtained by separating a raw starting product in a separatory device of a plant, which comprises the steps of substantially continuously measuring the content of said component in the fraction coming from the separatory device, separating from the measured fraction coming from the separatory device portions thereof having a content of said component higher than said predetermined value as determined by said measurement, mixing with portions of the measured fraction coming from the separatory device which have a content of said component lower than said predetermined value as determined by said measurement amounts of a material having a higher content of said component to obtain a mixture, substantially continuously measuring the content of said component in said mixture, and varying the amounts of succeeding portions mixed to obtain said mixture in accordance with said last mentioned measurement so as to insure that said mixture will have a substantially constant component content of said value.

2. Apparatus for preparing a final product of substantially constant quality, containing at least one component the content of which in the product is determinative of its quality, from a fraction, having a mean content of said component which substantially does not exceed a predetermined value, obtained by separating a raw starting product in a separatory device of a plant comprising means for substantially continuously measuring the content of the component in the fraction coming from the separatory device, a plurality of bunkers for receiving portions of the measured fraction, closure means for each bunker controlling the introduction of the fraction portions therein, means operable in response to the component content measured by said measuring means for actuating each closure means within different limited component content ranges so that each bunker will receive substantially only portions of said fraction having a component content with a given limited content range, means for selectively discharging said bunkers and means for mixing the fraction portions of differing component content selectively discharged from said bunkers so as to obtain a mixture of substantially constant component content of said value.

3. Apparatus as defined in claim 2 including means for measuring the content of said component in the mixture.

4. Apparatus for preparing a final product of substantially constant quality containing at least one component the content of which in the product is determinative of its quality comprising a separatory device for obtaining from a raw starting product a fraction having a mean content of the component which substantially does not exceed a predetermined value, means for substantially continuously measuring the content of the component in the fraction coming from said separatory device, means responsive to an output signal of said measuring means for separating from said fraction portions thereof hav ing a component content higher than said value, and means for mixing portions of said fraction having a lower component content than said value with material having a higher component content than said value to 12 obtain a mixture having a substantially constant component content of said value.

5. Apparatus as defined in claim 4 including a second separatory device for obtaining from a raw starting product a second fraction having a mean content of the component higher than said value, and means for supplying portions of said second fraction as said material into said mixing means.

6. Apparatus as defined in claim 5 wherein said second separatory device comprises a by-pass valve for preventing the first fraction portions of higher component content from entering said mixing means.

References Cited in the file of this patent UNITED STATES PATENTS 1,985,868 Maust Dec. 25, 1934 

1. A PROCESS OF PREPARING A VALUABLE FINAL PRODUCT OF SUBSTANTIALLY CONSTANT QUALITY, CONTAINING AT LEAST ONE COMPONENT THE CONTENT OF WHICH IN THE PRODUCT IS DETERMINATIVE OF ITS QUALITY, FROM A FRACTION, HAVING A MEAN CONTENT OF SAID COMPONENT WHICH SUBSTANTIALLY DOES NOT EXCEED A PREDETERMINED VALUE, OBTAINED BY SEPARATING A RAW STARTING PRODUCT IN A SEPARATORY DEVICE OF A PLANT, WHICH COMPRISES THE STEPS OF SUBSTANTIALLY CONTINUOUSLY MEASURING THE CONTENT OF SAID COMPONENT IN THE FRACTION COMING FROM THE SEPARATORY DEVICE, SEPARATING FROM THE MEASURED FRACTION COMING FROM THE SEPARATORY DEVICE PORTIONS THEREOF HAVING A CONTENT OF SAID COMPONENT HIGHER THAN SAID PREDETERMINED VALUE AS DETERMINED BY SAID MEASUREMENT, MIXING WITH PORTIONS OF THE MEASURED FRACTION COMING FROM THE SEPARATORY DEVICE WHICH HAVE A CONTENT OF SAID COMPONENT LOWER THAN SAID PREDETERMINED VALUE AS DETERMINED BY SAID MEASUREMENT AMOUNTS OF A MATERIAL HAVING A HIGHER CONTENT OF SAID COMPONENT TO OBTAIN A MIXTURE, SUBSTANTIALLY CONTINUOUSLY MEASURING THE CONTENT OF SAID COMPONENT IN SAID MIXTURE, AND VARYING THE AMOUNTS OF SUCCEEDING PORTIONS MIXED TO OBTAIN SAID MIXTURE IN ACCORDANCE WITH SAID LAST MENTIONED MEASUREMENT SO AS TO INSURE THAT SAID MIXTURE WILL HAVE A SUBSTANTIALLY CONSTANT COMPONENT CONTENT OF SAID VALUE. 